std::expected<T,E>:: value_or
From cppreference.net
|
Primary template
|
||
|
template
<
class
U
=
std::
remove_cv_t
<
T
>
>
constexpr T value_or ( U && default_value ) const & ; |
(1) | (since C++23) |
|
template
<
class
U
=
std::
remove_cv_t
<
T
>
>
constexpr T value_or ( U && default_value ) && ; |
(2) | (since C++23) |
Returns the expected value if it exists, otherwise returns default_value .
The void partial specialization does not have these member functions.
1)
If
std::
is_copy_constructible_v
<
T
>
or
std::
is_convertible_v
<
U, T
>
is
false
, the program is ill-formed.
2)
If
std::
is_move_constructible_v
<
T
>
or
std::
is_convertible_v
<
U, T
>
is
false
, the program is ill-formed.
Contents |
Parameters
| default_value | - | the value to use in case * this does not contain an expected value |
Return value
1)
has_value
(
)
?
**
this
:
static_cast
<
T
>
(
std::
forward
<
U
>
(
default_value
)
)
2)
has_value
(
)
?
std
::
move
(
**
this
)
:
static_cast
<
T
>
(
std::
forward
<
U
>
(
default_value
)
)
Example
|
This section is incomplete
Reason: no example |
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 3886 | C++23 |
U
does not have a default template argument
|
specified |
See also
|
returns the expected value
(public member function) |
|
|
returns the unexpected value if present, another value otherwise
(public member function) |